Al-Naysaburi said: How excellent is what Hammam narrated! He preserved it accurately and separated the words of the Prophet (peace and blessings be upon him) from the words of Qatadah. And in what reached me from Abu Sulayman al-Khattabi, from al-Hasan bin Yahya, from Ibn al-Mundhir, the author of al-Khilafiyyat, he said: This statement is from the fatwa of Qatadah; it is not part of the text of the hadith. Then he mentioned the hadith of Ali bin al-Hasan, from al-Muqri, from Hammam, and then said: Hammam has made known that the mention of the slave's working is from the words of Qatadah, while Sa'id bin Abi Arubah attached what Hammam had distinguished as the words of Qatadah and made it connected to the hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العتق / 21376